Microelectromechanic relay and method for the production thereof

ABSTRACT

The invention relates to a relay, especially a miniaturized electrostatic relay, comprising a bridge-type make contact. The contact spring is designed as a torsion spring that is linked with a switching spring ( 3 ) via multiply bent spring parts ( 7 ). It is thus possible in particular to compensate fixed contacts ( 2 ) of different heights. The invention further relates to a method for producing the relay as a micro-mechanical electrostatic relay.

The invention relates to a relay, in particular a micro-relay,comprising a bridge-type make contact. In addition thereto, theinvention relates to a method of making the relay.

The document DE 44 37 261 C1 discloses a micro-relay adapted to beproduced micromechanically, consisting of an etched-free silicon springtongue, which is pre-curved, and of a planar counter-electrode. Thespring tongue constitutes a wedge-shaped capacitor together with thecounter-electrode. By application of a control voltage between springtongue and planar counter-electrode, the spring tongue is stretcheduntil the free spring end touches the working contact on thecounter-electrode. During the switching operation, the curved springtongue rolls on the counter-electrode and thus forms a migrating wedge.

In addition to relays having a single closer or make contact function,in which the load current to be switched is conducted in a conductivetrack on the movable spring, there are desirable relays in which a makecontact constitutes a bridging contact across two fixed contacts. Thebridge-type make contact offers higher voltage strength and, in case ofhigh-frequency load current signals, a lower crosstalk capacity and thushigher frequency response. However, with bridge-type make contacts,there is the problem that the fixed contacts may be subject to wear todifferent extents, thereby making the switching strokes of theindividual fixed contacts different from each other. The result of thisis that there are different contact forces arising at the two fixedcontacts. Strong wear on one side would have the effect that one contactin the end would no longer close at all.

For realizing a bridge-type make contact with the aid of the knownmicro-relay, the movable spring tongue would have a rectangular contactarranged thereon, covering two fixed counter-contacts. Such anarrangement has the disadvantage that different contact forces arise incase of different wear of the two juxtaposed fixed contacts. Due to thehigh torsional rigidity of the spring tongue, the bridge contact cannotadjust to counter-contacts of different heights. In case of a furtherincreasing difference in height, one contact finally would no longer beclosed at all.

It is thus the object of the present invention to make available a relaywhich is adapted to be miniaturized and which establishes safe bridgingcontact also in case of different heights of the fixed contacts. Theinvention furthermore relates to a method of making the micro-relay.This object is met according to the invention by a relay according toclaim 1. Advantageous developments of the invention and a method ofmaking the invention are indicated in the further claims.

The invention indicates a relay comprising a base member with two fixedcontacts as well as a switching spring. The switching spring is attachedby way of an edge portion along a mounting line and is movable betweentwo positions, an open one and a closed one. In addition thereto, theswitching spring has a contact spring. Arranged on the contact spring isa movable contact bridging the fixed contacts when the switching springis in the closed position. Furthermore, the relay comprises a drivemember moving the switching spring and the contact spring between theopen and closed positions. The contact spring is in the form of atorsion spring that is rotatable about an axis of rotation. The axis ofrotation is located in the plane of the contact spring in the middlebetween the two fixed contacts. The projection of the axis of rotationonto the base member intersects the connecting line of the fixedcontacts substantially at right angles.

The effect achievable by the splitting of the relay spring into acontact spring and a switching spring, according to the invention, withthe contact spring being in the form of a torsion spring, is that safecontact is guaranteed also with different heights of the fixed contacts.Due to the rotatability of the torsion spring about an axis of rotationbetween the fixed contacts, the movable contact can adjust to differentheights of the fixed contacts. This is possible without impairing theswitching behavior of the switching spring.

Especially easy miniaturization is obtained with a relay according tothe invention in which the contact spring is part of the switchingspring.

The contact spring, in particularly advantageous manner, can be madefrom the switching spring in that portions of the switching spring areetched away. Such a procedure in particular provides for the possibilityof utilizing the patterning techniques known from silicon technology,with these being possibly transferred to a metallic switching spring.

A contact spring that is rotatable about an axis of rotation is attainedin particularly simple and thus advantageous manner by providing acontact part and one or more spring parts in the contact spring. Thecontact part constitutes the carrier of the movable contact and extendstransversely of the axis of rotation so as to cover the fixed contacts.This contact part is connected to the switching spring by one or morespring parts, with the spring parts being connected to the contact partin the region of the axis of rotation of the torsion spring. The effectachieved thereby is that the contact spring is a torsion spring and atthe same time is resiliently coupled to the switching spring.

In addition thereto, a development of the relay according to theinvention is particularly advantageous in which the shape of the springparts follows multiply curved paths. Due to this extended spring path,it is possible in particularly simple manner to obtain an arbitrary lowrigidity of the torsion spring, which facilitates tilting of the movablecontact so as to abut on two fixed contacts of different heights.

Furthermore, it is particularly advantageous to arrange the spring partson two opposite sides of the switching part, thereby ensuring that theaxis of rotation is not tilted due to unilateral mounting of the contactpart.

Moreover, it is particularly advantageous to design the relay in amanner in which the switching spring is attached to the base member andis curved away from the same. This renders possible the realization of arelay comprising a bridge contact with the initially indicated migratingwedge.

With this arrangement (with curved switching spring), it is particularlyadvantageous when the connecting line between the fixed contacts isparallel to the mounting line. Due to the fact that the switchingspring, in case of a relay making use of the migrating wedge principle,is urged onto a counter-piece starting from the mounting line, theeffect achieved by equal distances of the fixed contacts from themounting line is that the movable contact contacts the fixed contactsalmost simultaneously. For the same reason, such a relay employing thisarrangement of the fixed contacts, at all times has the same contactdistances between the fixed contacts and the movable contact.

It is particularly advantageous to choose an electrostatic drive asdrive member for the relay. Such a drive consists in that a firstelectrode, arranged on the side of the switching spring facing the basemember, and a second electrode, arranged on the base member opposite thefirst electrode, are connected to a dc voltage source. Such a driverequires energy for switching for short times only, whereas the closedposition is fixed solely by electrostatic interaction, withoutnecessitating the supply of additional energy.

In addition thereto, a relay is particularly advantageous in which theswitching spring consists of silicon and the base member consists ofsilicon or glass. Such a relay can be realized easily with thestructuring or patterning and manufacturing techniques known fromsilicon technology.

The invention furthermore indicates a method of making such a relay,comprising the following steps:

1. The second electrode and the fixed contacts are deposited on the basesubstrate constituting the base member and then are patterned.

2. Thereafter, an insulating layer is deposited on the second electrode.

3. A silicon wafer having a doped silicon layer on the side of the waferfacing the base substrate is bonded onto the base substrate.

4. Beginning from the side of the silicon wafer facing away from thedoped silicon layer, said wafer is etched back, e.g. by KOH etching,until the doped silicon layer is left standing that is to form theswitching spring.

5. Finally, by patterning of the doped silicon layer, the contact springis formed from the switching spring or the switching spring itself isformed, respectively.

Such a method has the advantage that miniaturized relays can bemanufactured very easily.

In the following, the invention will be elucidated in more detail by wayof embodiments and the associated drawings.

FIG. 1 shows the switching spring of a relay according to the invention,in which the connecting line of the fixed contacts extends parallel tothe mounting line, in a schematic plan view.

FIG. 2 shows the switching spring of a relay according to the invention,in which the connecting line of the fixed contacts is perpendicular tothe mounting line, in a schematic plan view.

FIG. 3 shows a relay with migrating wedge according to the invention inthe open state, in a schematic longitudinal sectional view.

FIG. 4 shows a relay with migrating wedge according to the invention inthe closed state, in a schematic longitudinal sectional view.

FIG. 1 shows the switching spring 3 of a relay according to theinvention, which is attached along mounting line 11. The switchingspring 3 comprises a contact spring 4 consisting of a contact part 6 andspring parts 7. Spring parts 7, with respect to the shape thereof,follow multiply curved paths. The torsional rigidity may thus beadjusted to any desired low value. Starting from both sides of thecontact part 6, the spring parts connected the latter to switchingspring 3, thus ensuring that the axis of rotation 12 is not tilted dueto unilateral mounting of contact part 6. On the bottom side of contactpart 6, there is disposed the movable contact 5 (FIG. 3). The fixedcontacts 2 of the base member, not shown, are arranged underneathcontact part 6. Contact part 6 is rotatable about the axis of rotation12. The axis of rotation 12 is perpendicular to the mounting line 11.The fixed contacts 2 are arranged underneath the contact part 6 on bothsides of said axis of rotation 12.

FIG. 2 shows the switching spring 3 of a relay according to theinvention, which is attached along mounting line 11. Switching spring 3has a contact spring 4 consisting of contact part 6 and spring parts 7.Spring parts 7, with respect to the shape thereof, follow multiplycurved paths. The torsional rigidity may thus be adjusted to the desiredlow value. Starting from opposite sides of the contact part 6, thespring parts connect the latter to switching spring 3, thus ensuringthat the axis of rotation 12 is not tilted due to unilateral mounting ofcontact part 6. On the bottom side of contact part 6, there is disposedthe movable contact 5 (FIG. 3) . The fixed contacts 2 are arrangedunderneath contact part 6. Contact part 6 is rotatable about the axis ofrotation 12. The axis of rotation 12 is parallel to the mounting line11. The fixed contacts are arranged underneath the contact part on bothsides of said axis of rotation 12.

FIG. 3 shows a relay with migrating wedge, according the invention, inthe open state. The migrating wedge is constituted of the base member 1and the switching spring 3 which is curved away from the latter, butotherwise is formed identically as in FIG. 2. Arranged on the basemember 1 are the fixed contacts 2 as well as the second electrode 9having an insulating layer 10. The switching spring 3, on the left-handedge thereof, is fixed connected to base member 1. The switching spring3 comprises a first electrode 8 as well as the spring part 7 and thecontact part 6 of the contact spring. Contact part 6 is rotatable aboutthe axis of rotation 12. Furthermore, the contact part 6 has a movablecontact 5 on its bottom side. The rotatable contact part 6 may easilyadjust to fixed contacts 2 of different height and thus provide for safecontacting. In the present example, the fixed contacts 2 are arrangedsuch that their connecting line is perpendicular to mounting line 11.This has the effect that, in closing the relay, contact is establishedfirst with the left-hand one and then with the right-hand one of thefixed contacts 2. In addition thereto, the contacting distance of theleft-hand fixed contact 2 is at all times smaller than the contactingdistance of the right-hand fixed contact 2 (except in the closedcondition).

FIG. 4 illustrates the relay of FIG. 3 in the closed state. Theswitching spring 3 abuts on base member 1. The contact part 6, raised byway of switching spring 3, abuts the fixed contacts 2. The spring parts7 connect the switching spring to the contact spring and establish thecontacting force between movable contact 5 and fixed contacts 2.

The invention is not restricted to the embodiments shown in exemplaryform, but is defined in its most general form by claim 1.

What is claimed is:
 1. A relay, comprising: a base member having twofixed contacts, a switching spring attached by way of an edge portionalong a mounting line, said switching spring being movable between openand closed positions and having a contact spring, a movable contactarranged on the contact spring and bridging the fixed contacts in theclosed position of the switching spring, a drive member moving theswitching spring and the contact spring between said open and closedpositions, wherein said contact spring is designed as torsion springthat is rotatable about an axis of rotation arranged centrally andperpendicularly to the connecting line between the fixed contacts andlocated in the plane of the contact spring.
 2. A relay according toclaim 1, wherein said contact spring is part of said switching spring.3. A relay according to claim 2, wherein the contact spring ismanufactured by etching away portions of said switching spring.
 4. Arelay according to claim 2, wherein the contact spring consists of acontact part extending transversely to the axis of rotation, and of oneor more spring parts connected both to the contact part and to theswitching spring in the region of said axis of rotation.
 5. A relayaccording to claim 4, wherein the configuration of the spring partsfollows multiply curved paths.
 6. A relay according to claim 4, whereinthe spring parts start from opposite sides of the contact part.
 7. Arelay according to claim 1, wherein the switching spring is attached tothe base member and is curved away from the same.
 8. A relay accordingto claim 1, wherein the fixed contacts are arranged such that theirconnecting line is perpendicular to said mounting line.
 9. A relayaccording to claim 1, wherein the fixed contacts are arranged such thattheir connecting line is parallel to said mounting line.
 10. A relayaccording to claim 7, wherein the drive member comprises a firstelectrode arranged on the side of the switching spring facing the basemember, a second electrode arranged on the base member opposite thefirst electrode, and a dc voltage source connected to the electrodes.11. A relay according to claim 8, wherein the drive member comprises afirst electrode arranged on the side of the switching spring facing thebase member, a second electrode arranged on the base member opposite thefirst electrode, and a dc voltage source connected to the electrodes.12. A relay according to claim 9, wherein the drive member comprises afirst electrode arranged on the side of the switching spring facing thebase member, a second electrode arranged on the base member opposite thefirst electrode, and a dc voltage source connected to the electrodes.13. A relay according to claim 1, wherein said switching spring consistsof silicon and said base member consists of silicon or glass.
 14. Arelay comprising a base member having two fixed contacts, where aswitching spring is attached by way of an edge portion along a mountingline, said switching spring having a contact spring and being movablebetween open and closed positions, a movable contact arranged on thecontact spring and bridging the fixed contacts in the closed position ofthe switching spring, a drive member moving the switching spring and thecontact spring between said open and closed positions, said contactspring being profiled as a torsion spring linked to said switchingspring via multiply bent spring sections.
 15. A relay according to claim14, wherein said torsion spring is rotatable about an axis of rotationarranged centrally and perpendicularly to the connecting line betweenthe fixed contacts and located in the plane of the contact spring.
 16. Arelay comprising a base member having two fixed contacts, where aswitching spring is attached by way of an edge portion along a mountingline, said switching spring having a contact spring, and said switchingspring being movable between open and closed positions, a movablecontact arranged on the contact spring and bridging the fixed contactsin the closed position of the switching spring, a drive member movingthe switching spring and the contact spring between said open and closedpositions, said contact spring having torsion spring means forcompensating said contact spring to various heights of said fixedcontacts.
 17. A relay according to claim 16, wherein said contact springis profiled as a torsion spring linked to said switching spring viamultiply bent spring sections.
 18. A relay according to claim 16,wherein said torsion spring means is rotatable about an axis of rotationarranged centrally and perpendicularly to the connecting line betweenthe fixed contacts and located in the plane of the contact spring.
 19. Arelay according to claim 16, wherein the contact spring consists of acontact part extending transversely to an axis of rotation, and of oneor more spring parts connected both to the contact part and to theswitching spring in the region of said axis of rotation.
 20. A method ofmaking a relay, having a base member having two fixed contacts, aswitching spring which is movable between open and closed positions andhaving a contact spring, a movable contact arranged on the contactspring and bridging the fixed contacts in the closed position of theswitching spring, and a drive member comprising a first electrodearranged on the side of the switching spring facing the base member, anda second electrode arranged on the base member opposite the firstelectrode, the method of comprising the steps of: a) depositing thesecond electrode, an overlying insulating layer and the fixed contactson a base substrate constituting the base member, b) bonding a siliconwafer, having a doped silicon layer on the side of the wafer facing thebase substrate, onto the base substrate, and c) patterning the dopedsilicon layer to form the switching spring and the contact spring.